When setting up merge replication on your SQL 2008 + server, please be careful with the parameter STREAM_BLOB_COLUMN.
By default, this option is set to FALSE, as explained here in BOL:
[ @stream_blob_columns= ] 'stream_blob_columns' Specifies that...

Problem:
If sql_variant column includes a value with new datetime type, the value is replicated as base type nvarchar even if schema option 0x200000000 is not set during the application of the SNAPSHOT (only).
After the snapshot has been applied...